Start implementing grow merkle fn

eth2/utils/ssz/src/cached_tree_hash/impls.rs

@@ -170,6 +170,23 @@ where
     }
 }
 
+/// New vec is bigger than old vec.
+fn grow_merkle_cache(cache: Vec<u8>, to: usize) -> Vec<u8> {
+    let new = Vec::with_capacity(to * HASHSIZE);
+
+    let i = cache.len() / HASHSIZE;
+    let j = to;
+
+    assert_eq!(i.next_power_of_two(), i);
+    assert_eq!(j.next_power_of_two(), j);
+
+    while i > 0 {
+        
+    }
+
+    new
+}
+
 fn get_packed_leaves<T>(vec: &Vec<T>) -> Vec<u8>
 where
     T: CachedTreeHash<T>,